{- Exercise 11.1 -}
validBrackets :: String -> Bool
validBrackets = undefined


{- Exercise 11.2 -}
longestPalindrom :: Eq a => [a] -> [a]
longestPalindrom xs = undefined


{- Exercise 11.3 -}
data Tree a = Empty | Node (Tree a) a (Tree a)

validBST :: Ord a => Tree a -> Bool
validBST = undefined


{- Exercise 11.4 -}
addNumbers :: IO ()
addNumbers = undefined


{- TESTS -}
testValidBrackets = all (\(t, s) -> (t == validBrackets s))
  [(True, "(a[bc])"), (True, "(){ab}c"), (False, "({ab)}c")]

testLongestPalindrom = all (\(s, p) -> longestPalindrom s == p)
  [("xabai", "aba"), ("hannah steht neben dem regallager.", "regallager")]

testValidBST = all (\(t, s) -> (t == validBST s))
  [(True, Empty)
  ,(False, Node (Empty) 5 (Node (Node Empty 4 Empty) 9 Empty))
  ,(True, Node (Node Empty 4 Empty) 5 (Node Empty 8 Empty))]